Piano soundboard



1941- R. w. CARLISLE PIANO SOUNDBOARD Filed Jan. 2, 1937 Patented Jan.21, 1941 UNITED STATES PATENT OFFlQE PIANO SOUNDBOARD ApplicationJanuary 2, 1937, Serial No. 118,862

6 Claims.

This invention relates to musical instruments and soundboards as usedtherein, and more particularly in pianos, harps, violins and otherinstruments, in which a more or less flat, stiff soundboard is commonlyused.

It is one object of this invention to greatly increase the acousticefliciency of any given size of soundboard, especially with respect tolow frequencies.

It is another object of this invention to provide means for constructinga musical instrument of any given class with a soundboard cnsiderablyreduced in size without reducing its acoustic output.

It is another object of this invention to improve the purity of waveform of certain notes by preventing deleterious absorption of energyfrom the edge of a diaphragm into a frame or case structure.

It is another object of this invention to construct a musical instrumentof the heavier class such as the piano with a cost greatly reduced byreason of the economies effected through the lightening of the casestructure which is possible when using my invention.

The manner in which this invention attains these objects is illustratedwith specific application to a piano in the accompanying drawing, inwhich Fig. 1 is a plan view of a part of a piano soundboard Fig. 2 is asection through the line 22 of Fig. l and the line 22 of Figure 6 Fig. 3is part of a cross section through the line 33 of Fig. 1, and also asection through the line 3-3 of Fig. 2; and

Fig. 4 is an enlargement of the section through 4-4 of Fi 2.

Figure 5 is an end section view of the treble part of my soundboardthrough the line 55 of Figure 6, and

Figure 6 is a schematic plan view of a piano soundboard constructedaccording to my invention.

In the drawing referring first to Figs. 1 and 2, the strings I are showndisposed in spaced relationship to a soundboard 3. Each string isaffixed at each end thereof to a relatively rigid metal string plate 5.A part of this string plate 5 is extended around'the edge of thesoundboard 3 to form a frame 5' for the edge of said soundboard as shownin Fig. 2. Between the underside of said soundboard 3 and the uppersurface of said frame 5' is interposed a resilient cushion required toencompass the strings, it follows that 10 the bridge 9 must necessarilybe located close to one edge of the frame 5. The soundboard 3 iscustomarily reinforced with ribs as shown at 1 and 7'. At extreme lowfrequency it is desirable to secure the greatest possible amplitude ofvibration over the largest possible area. In this manner the maximumsound radiation may be attained, since radiation from a surface isproportional to the product of the surface area and the velocity ofvibration. The soundboard is vibrated by the strings I which vibrateagainst the bridge 9, the vibrations being carried to the soundboard 3and causing the soundboard to vibrate. If a soundboard is not madeflexible around its periphery only a small amplitude of vibration willoccur; if it be made flexible around the entire periphery, or if it besuspended on a resilient cushion around the entire periphery, a largeamplitude of vibration will occur in the immediate vicinity of thebridge but will not spread therefrom over the entire diaphragm at lowfrequencies because the diaphragm will tend to rock about its center andonly the edge will move. If, however, in accordance with my invention asshown in Figure 6 that part of the edge 30-3l to which the bridge 9 isadjacent to be pivotally supported on the surface H], the ribs will actas levers to transmit the motion of the bridge 9 to the central portionof the soundboard 3, provided that the far side 3|, 32, 33, 34 isresiliently supported as shown in Figure 2 at 6. It is advantageous tomake the pivoted side heavier, and the far side lighter, in order toimprove this pivoting action.

As is customary in the art, a fibrous soundboard may be used having thegrain thereof running substantially perpendicular to the bass strings,as shown in Fig. 1.

One manner in which pivotal support may be accomplished as shown inFigures 2 and 3 in which strips of wood I0 and I3, rounded at the top asshown in Fig. 2, are placed under the ribs 1 and 1, respectively, on theframe 5'. Strips II and II may be placed between said ribs and fittedbetween the frame 5' and the bottom surface of the soundboard 3, andhaving the surface juxtaposed to said soundboard rounded in the samemanner as that of the strip it.

A resilient cushion may be used as shown at 6 in Fig. 2 around any partof the periphery of the soundboard 3 or all of said periphery,preferably excepting the region 3" adjacent to the low frequency bridge9 in Figures 1 and 6, as located between and 3! as shown in Figure 6. Inone embodiment this resilient support of the soundboard 3 upon the frame5' is secured by the use of one or more layers of a resilient,continuously undulating strip I2. To avoid audible vibrations thereinstrips of fabric l3 and I4 as shown in Fig. 4 may be placed immediatelyabove and below it respectively. Loose felt or cotton wadding [5 mayalso be interposed in the interstices above and below the spring [2 toprevent leakage of air around the edge of the soundboard, which wouldcause a certain loss in low frequency radiation. It is also possible todamp vibrations of the edge of the diaphragm by inserting more of suchdamping material. This is particularly useful around the treble end ofthe soundboard 34, 3E, 36 of Figure 6; the tone quality of the radiatedsound depends to a considerable extent upon providing exactly the rightwidth of soundboard and properly damping the edges thereof.

Furthermore, the excessive damping which has previously been placed upontreble ends of soundboards due to their rigid attachment to the case 2 3is obviated by the resilient connection means herein provided. Thispermits the radiation of purer and more sustained tones. It also permitseconomies in case construction since variations in said case will notaffect the performones.

In order that the soundboard to may be very narrow at the treble end ofthe soundboard, the

frame 5' may be extended inwardly as shown at 25 and 2b in Fig. 5 sothat the strings may have over a length greater than the width of thesoundboard.

As shown in Fig. 5 the soundboard 3d at the treble end of the instrumentshould be made of relatively thinner and harder material than theremainder of the soundboard. Furthermore, the bridge connecting thetreble strings to this small, hard and stiff portion of the soundboardshould be extremely light and stiff, as indicated by the narrow bridgeto in Fig. 5. The degree of resiliency and damping of the mounting ofthe edges of the soundboard 13a to said extensions .25 and 243 may byuse of the means illustrated in Figs. 3 and 4 be predetermined to secureany desired degree of sustenance of high frequency tone.

Any elongated member of a resilient nature may be utilized around theperiphery of the soundboard such as rubber tubing or other flexibletubing. This may be varied in flexibility and in damping qualities asdesired around the periphery of the soundboard.

The soundboard shown in the drawing is customarily crowned and flexed,as Well known in the piano art.

Although pianos are customarily constructed with flexed strings asresonators, they are sometimes constructed utilizing tuning forks, aswell known in the art. The soundboard constructed herein described isequally applicable to use with resonators other than string-s.

In one embodiment of my invention, a piano soundboard is mounted on aflexible suspension comprised of two layers of corrugated steel strip.009 inch thick and inch wide at all points around the periphery exceptthat part adjacent to the bass bridge. The ratio of the deformation atthe center of the soundboard to the force applied on the soundboard bythe strings is .091 inch per pound, whereas without the flexiblesuspension the stiffness due to the flat soundboard alone Without therib supports is .05G, showing nearly a 2 to 1 improvement in flexibilityand a consequent improvement in low frequency efficiency. This featureof added flexibility becomes increasingly important as the size of aninstrument is reduced.

1 claim:

1. In .a piano, a soundboard pivotally supportalong the edge adjacent tothe bridge and flexibly supported along other edges, means forre-inforcing said soundboard, said means bein stiffer along saidpivotally supported edge than along the flexibly supported edges.

2. In a piano, a soundboard pivotally supported along the edge adjacentto the bridge and flexibly supported along other edges, the side of saidsoundboard opposite to said pivoted edge being lighter in weight thanthe pivotally supported side.

3. In a piano, a fibrous soundboard having the grain thereof runningperpendicular to the strings, a bridge on said soundboard near one edgethereof, reinforcing ribs on the soundboard perpendicular to said grainand means for pivotally supporting said soundboard along the edgeadjacent to said bridge, and means for flexibly supporting saidsoundboard at the ends of the aforementioned grain.

4. In a musical instrument, a flexed soundboard supported around itsedge by means comprised of a metal spring strip having an undulatingshape and a compressible damping material disposed around the springstrip, said damping material controlling vibrations of the edge of thesoundboard.

5. In a piano a frame having a rigid fulcrum thereon, a soundboardpivoted on said fulcrum and resilient means on the frame for supportingthe opposite end of the soundboard yieldably to accommodate pivotalmounting about the fulcrum and a bridge mounted on the soundboardadjacent said rigid fulcrum.

6. A soundboard having a bass and treble por tion, rigid supportingmembers under each edge of the treble portion, resilient meansinterposed intermediate said supporting member and said treble portion,means pivotally supporting said soundboard at a point remote from saidtreble portion, and means positioned intermediate said resilient meansand said treble portion of said soundboard for modifying the resilienceand damping effiect of said resilient means.

RICHARD W'ALLACE CARLISLE.

